1. Field of the Invention
The present invention relates generally to a test method for detecting operational errors of the tester used for testing the electrical conditions of semiconductor devices. More particularly, the present invention relates to a test method for detecting operational errors of the tester, in which a failed device is erroneously sorted as a good one, using a diagnosis program.
2. Background of the Related Art
In general, semiconductor devices are subjected to various tests of the reliability of their electrical performance. The testing items can be varied depending on the type of semiconductor devices to be tested.
The test procedure employed for memory semiconductor devices in particular may be divided into two groups: first, direct current (DC) items for testing DC parameters, for example, the electric power consumption of the devices; and second, alternating current (AC) items for testing AC parameters such as the data storing performance of the devices. The AC tests are particularly important for memory devices, the main function of which is to store data. The AC tests are carried out by writing data to the device to be tested at various timings, voltage levels and patterns, and examining whether or not the written data can be retrieved intact. The tester used for this purpose will be described below.
FIG. 1 is a block diagram of a conventional test system 50 comprising a tester 51 for checking the electrical performance of the device to be tested and a handler 53 for loading/unloading the device to/from the tester 51. The operations of the tester 51 and of the handler 53 are controlled by a test program (not shown), and the tester 51 is electrically connected to the handler 53.
When the tester 51 transmits a signal to the handler 53 for starting the test, the handler 53 picks up the device to be tested and electrically connects it to the tester 51. Then, the tester 51 inputs the electrical test signal into the device and measures the output from the device, thereby determining whether the device is good (passed) or failed according to the test program. The handler 53 unloads the device from the tester 51 and sorts it as passed or failed depending on the results.
In this way, accurate tests on the memory devices can be carried out by using the test system as described above, so long as the tester itself is operating properly. However, like any other piece of equipment, the tester may be out of sequence, encounter electrical or mechanical trouble, or experience some other operational error.
The predominant error is that a good device is sorted as a failed one because of an operational error of the tester. This type of error does not have a significant effect on the yield of the test process, since the failed devices are usually subjected to a retest to determine the cause of the failure. Thus, devices that pass the retest are sorted as good devices. Also, the operator or engineer generally stops and checks the tester to locate any operational error when many failures occur for a certain test item.
On the other hand, when a failed device is sorted as a good one due to an operational error of the tester, the failed device causes irreparable damage to the quality control of the devices. Moreover, for such a case, the erroneously sorted good device is not subjected to a retest, and the operational error of the tester will not be detected.
In the test process, a diagnosis program provided by tester manufacturers is performed to detect any operational errors of the tester. However, the diagnosis program has a limitation, because it only checks the internal operation of the tester without using output data from the device. Moreover, different diagnosis programs are required for different memory semiconductor devices having different functional, operational and voltage conditions and different internal operation modes. Further, the diagnostic test using an auto-detection program requires a relatively long period of time. For example, it takes the T5581H model tester (ADVANTEST) about 3 hours to complete a diagnostic test using an auto-detection program.